The present invention relates to an apparatus for producing crystalline materials and more particularly to an apparatus for producing high-melting-metal-oxide-based crystalline materials by melting and which may find application in the ceramic industry for manufacturing high-melting-metal-oxide-based high-temperature ceramics.
Different methods of producing high-melting-metal-oxide-based crystalline materials and devices for effecting the methods are known in the art.
Thus, in one of the prior-art methods of producing high-melting-metal-oxide-based crystalline materials adapted for manufacturing high-temperature ceramics a charge comprising high-melting metal oxides is mixed, pressed and subjected to a prolonged annealing at a temperature far below the above melting point of the above oxides.
Also known is a device for effecting the method of producing high-melting-metal-oxide-based crystalline materials. The device is shaped as a flame furnace whose body is made of metal lined inside with ceramics and is furnished with burners intended to feed fuel into the furnace inner space, wherein the charge is exposed to prolonged annealing under the effect of the fuel being burned.
Since the charge is subjected to an irregular effect of a heat field, the thus-obtained crystalline material contains unreacted constituents, this adversely affects the properties of the produced material and is a disadvantage of the above-mentioned procedure. In another known method of producing high-melting-metal-oxide-based crystalline materials by melting, adapted essentially also for manufacturing ceramics based on the above oxides, a charge composed of high-melting metal oxides is, upon mixing, subjected to arc melting.
The known device for effecting the known method is an electric arc furnace whose body is made from metal lined within with ceramics and provided with graphite electrodes between which an arc discharge occurs which melts the charge.
A serious disadvantage peculiar to this method of producing high-melting-metal-oxide-based crystalline materials by melting and to the device for carrying out the method resides in that when graphite electrode are employed some high-melting oxides interact chemically with the electrode material in the course of arc discharge, forming carbides or are reduced to a metal and thus contaminate the crystalline material obtained.
Finally, another known method of producing high-melting-metal-oxide-based crystalline materials by melting, comprises the steps of: loading a charge whose composition incorporates at least one high-melting metal oxide into a cooled mould which is a container, introducing an oxide-forming metal into the loaded charge in amounts providing for the initial melting of the charge and subsequent melting of said charge under the effect of a high-frequency electromagnetic field, with the container being withdrawn together with the molten material out of the zone of action of the high-frequency electromagnetic field and cooled with water, with the crystalline material produced being, on completion of crystallization, cooled in the container and, on being unloaded therefrom, in air.
Also known is a device for effecting the above outlined prior-art method of producing high-melting-metal-oxide-based crystalline materials by melting, comprising a cooled mould with a port for loading the charge, with the mould body being made as a container built up of several copper water-cooled tubes mounted on an insulating plate, spaced at a distance of 1-2 mm from each other and surrounded by an inductor generating a high-frequency electromagnetic field, with a charge-loading means being disposed at the mould port and a means provided for the withdrawal of the crystalline material together with the container.
The thus-obtained crystalline material does not comprise unreacted metal oxides and features a high purity of its chemical composition attributable to the fact that there is no contact whatever between the melt and container walls which are always separated therefrom, owing to water cooling, by a layer of unmelted charge, the so-called wall accretions.
However, one of the essential disadvantages inherent in the known method and device for its realization consists in that the crystalline material obtained does not feature a high degree of homogeneity, this stems from the disadvantages of the crystallization process which takes place in such a container.
Moreover, the apparatus suffers from another disadvantage, i.e. low efficiency related to the inherent design drawbacks of the mould requiring a prolonged multi-stage nature of the process of producing the crystalline material.